Forage grass-legume mixture for improved forage yield, forage quality, stand persistence, soil properties, and economics

Field studies were established at two locations (Lingle and Laramie, Wyoming) with two planting (fall and spring) seasons with five specific objectives: 1) to compare forage yield, forage quality, and stand persistence of different grass-legume mixtures; 2) to identify the optimum seeding proportion of grass and legume for obtaining improved yield and stand persistence; 3) to study soil carbon (C) and nitrogen (N) dynamics under different seeding proportions of grass and legume; 4) to assess the effect of different seeding combinations of grass and legume on soil microbial biomass and their community structure; and 5) to compare net economic return from different seeding proportions of grass and legume. Different mixture ratios of a forage legume (alfalfa, Medicago sativa L.), and two cool-season perennial forage grasses (meadow bromegrass, Bromus biebersteinii Roem. & Schult. and orchardgrass, Dactylis glomerata L.) were established for the study. Sixteen different treatment combinations included monoculture grass, monoculture legume, two grass mixtures, one grass and one legume mixtures, and two grasses and one legume mixture. Monoculture grass and two grass mixtures received either no N or N fertilizer (0 and 150 kg N ha-1 yr -1 as urea) whereas monoculture legume and grass-legume mixtures received no N fertilizer. The experiment was laid out as randomized complete block design with three replicates under irrigation. The 50-50% mixture ratio of alfalfa-meadow bromegrass from fall planting and 50-50% mixture ratio of alfalfa-orchardgrass from spring planting produced the highest total forage dry matter (DM) yield among the treatments during the study period. Same treatments provided with higher forage quality compared to grass with 150 kg N ha-1 yr-1. The 50-50% mixture of alfalfa-meadow bromegrass provided with the best stand persistence over 4-yr study period. The labile pool of soil organic matter (SOM) such as mineralizable C and N, inorganic N, and total N were increased when alfalfa was included in the mixture as 50% seeding ratio compared to only grass, although total soil organic carbon (SOC) was not changed during the study period. Soil microbial biomass and community structure were also improved from 50-50% mixture of grass-alfalfa compared to no N or N fertilizer grass. The inclusion of 50% alfalfa in mixture with grass also improved net economic return compared to monoculture of both grass and legume. The study demonstrated that inclusion of 50% alfalfa in forage grass would be beneficial in terms of forage yield, forage quality, stand persistence, soil properties, and net economic return.